The invention relates to a device for controlling the charging of rechargeable batteries comprising electric means for supplying charging current to the battery, a first temperature sensor sensitive to the temperature of the battery, a second temperature sensor sensitive to the ambient temperature and a device for stopping the charging at the end of the charging operation and controlled by the first and second sensors.
At the end of the process of charging the rechargeable batteries, especially nickel-cadmium batteries, a very high increase of pressure and an increase in temperature occur. If the charging is not stopped in time, this may lead to a rapid deterioration of the batteries by overpressure and/or by an excessively high temperature. This increase in temperature becomes very rapid at the end of the charging operation when the charge approaches 100 % of the battery capacity. It is therefore necessary to stop the charging when the charge approaches this maximum value.
A suitable method consists in tracking the temperature of the battery. A charging device which has effected this operation is known from the document U.S. Pat. No. 4,370,606 in which the temperature sensors, which are diodes or thermistors, become active according to different laws of compensation in an electronic circuit acting upon the charge stopping device.
Now, the temperature sensors used according to this document are discrete elements having a non-negligible volume. They have to be disposed in a mechanical support with the result that their thermal contact is of low quality. This also applies to the case in which these elements are used in an isolated manner.